How does a Fire Tube Boiler work?| What are types of Fire Tube Boilers?

The boiler is a mechanical device used for steam generation. The boilers are used in different household and industrial applications. There are multiple types of boilers that are designed according to the application requirements. A fire-tube boiler is the most common type of boiler. The boilers have two major types:

  1. Water-tube boiler
  2. Fire-tube boiler

In the previous article, we discussed the water tube boiler. Therefore, in this article, we are going to discuss the fire tube boiler.

What is a Fire Tube Boiler?

A fire-tube boiler is a boiler in which fire tubes are immersed in water, and the hot flue gases produced by the combustion chamber flow inside the fire tubes. The hot flue gases transfer their heat to the outside water through the conduction process. When heat transfers to the water, it converts into steam.

Fire Tube Boiler

These types of boilers are most commonly utilized for applications that require low to medium steam pressure and a low rate of steam generation. A fire-tube boiler is not best for applications that require a high rate of steam applications. These boilers can generate steam pressure up to 10 Kg/cm2 and steam production rate up to 12,000 Kg/hr.

The fire tube boiler has a furnace, grate, combustion chamber, chimney, fire tubes, and smokebox. The chimney uses to discharge the waste gases and smoke into the atmosphere.

They have the capability to uses multiple fuels such as gaseous, coal, liquid/oil, or solid fuels.

Working Principle of Fire Tube Boiler

The working of the fire tube boiler is very similar to the water tube boiler. A fire-tube boiler works in the following way:

  • First of all, a feed pump pumps water into the boiler.
  • The grate is used to place the coal fuel.
  • The fire is introduced into the furnace through a fire hole.
  • As the fire ignites the fuel, the heat is produced.
  • The produced heat transfers to the flue gases.
  • When the temperature of the flue gases increases, they start moving into the combustion chamber.
  • After passing through the combustion chamber, the hot gases enter the fire tubes.
  • The fire tube submerges into the water.
  • The flue gases deliver their heat to the water through the conduction process.
  • As the water receives heat, its temperature increases; due to that, it transfers into saturated steam.
  • You may use this saturated steam directly or may use it after converting saturated steam into superheated steam.
  • The yield steam is transferred to the steam turbine, where it rotates the turbine blades and generates electricity.
  • A superheater uses for transforming saturated steam into superheated steam.

Types of Fire Tube Boilers

The fire tube boiler has the following major types:

  1. Velcon boiler
  2. Scotch marine boiler
  3. Cornish boiler
  4. Cochran boiler
  5. Simple vertical boiler
  6. Locomotive boiler
  7. Lancashire boiler

1) Cochran Boiler

It is an internally fired, low pressure, and vertical drum air boiler. These boilers are not best for high-pressure steam applications.

The Cochran boiler is a portable boiler. You can easily shift it from one place to another. It is a modified version of the simple vertical boiler.  This type of fire tube boiler can only use oil or coal fuel for producing hot gases. The Cochran boiler is best for small industries and power plants.

Cochran Boiler Working

The Cochran boiler has horizontally fire tubes. It has 165 fire tubes. It is more efficient than a simple vertical boiler. One of the big advantages of the Cochran boiler is that it has a small size due to that it can easily install in a small space.

Read Also: Working of Cochran Boiler 

2) Cornish Boiler

The Cornish boiler is a type of boiler that can produce steam pressure up to 20 bar. It has a steam generation rate of up to 6500 kg/hour. This boiler also has a small size, and you can easily transfer it from one area to another.  The Cornish boiler has a shell that has a length from 4m to 7m and a diameter from 1.2m to 1.8m. It has only one fire tube.

Cornish Boiler

The advantage of the Cornish boiler is that it has a very simple design, low maintenance cost, easy construction, and is portable. It is most commonly used in the chemical industry, sugar mills, and small hydropower plants.  These boilers also use to run steam turbines.

3) Locomotive Boiler

A locomotive boiler is a mobile boiler (i.e., a portable boiler). It is an externally fired boiler. This boiler has a horizontal axis drum, large fire space, and multiple tubes.

This type of boiler has a grate, furnace, ashpit, feed pump, smokebox, chimney, and fire tubes. The grate is the place where solid coal is placed, and the ashpit uses to collect the ash of the burnt fuel.

Locomotive boiler

The locomotive boilers were used in the Locomotive engines, but nowadays, these engines are driven by electricity or diesel fuel. These boilers were used in railway engines up to the 20th century, but later they converted to fuel engines and now electricity.

These boilers are most commonly used in portable steam engines, traction engines, marines, and railways.

The most important advantage of the locomotive boiler is that it has a high rate of steam generation. However, it has low overall efficiency. 

Read More: Working and Construction of Locomotive Boiler 

4) Horizontal Return Tubular Boiler (HRT)

This boiler has a horizontally cylindrical shell that has many flue tubes arranged in a horizontal direction. This boiler has a low initial cost. It also has an easy installation.

Horizontal return tubular fire tube boiler

The HRT boiler has the capability to use gas, wood, oil, or coal fuels. In this boiler, the flue gases flow from the firebox to the rear of the boiler.

5) Lancashire Boiler

This type of fire tube boiler has the same operation as Cornish boiler, but it has two large flues that contain fires. In 1884, William Fairbairn designed the Lancashire boiler.

The Lancashire boiler is an internally fired natural circulation boiler. This boiler has a furnace inside the boiler.  

Lancashire boiler construction

The main advantage of this boiler is that it has high thermal efficiency (from 80% to 90%).  The Lancashire boiler has working pressure up to 16 bar. It consumes low electricity or other fuel because it has a natural circulation of steam.

These types of boilers are most commonly used in tire industries, sugar industries, textile industries, and paper industries.

Read Also: Working of Lacashire Boiler 

6) Simple Vertical Boiler

The simple vertical boiler installs in a vertical direction, and it doesn’t remain in a stationary condition, unlike other fire tube boilers. It has a low steam generation rate. It is not best for high steam pressure applications. Therefore, these boilers are used in low steam generation applications.

Simple Vertical Boiler

The vertical boiler has a small size. Therefore, it needs low space for installation. The big advantage of this fire tube boiler is that it needs low cost and space for installation. It has a simple operation and is very easy to replace or install. 

The vertical fire tube boilers use in steam donkeys, steam locomotives, steam shovels, railway steam engines, steam lorry, and steam cranes. 

Fire Tube Boiler Parts and Functions

The fire tube boiler has the following parts:

  1. Ashpit
  2. Furnace
  3. Grate
  4. Fire tubes
  5. Chimney
  6. Combustion chamber
  7. Firebox
  8. Smokebox
  9. Fire hole
  10. Manhole
  11. Feed Pump

Advantages and Disadvantages of Fire Tube Boiler

The advantages and disadvantages of the fir tube boilers are given below:

Advantages of fire tube boiler

  • This boiler has easy maintenance and cleaning.
  • It has a simple operation.
  • It is best for small industrial applications.
  • The fire tube boiler has low cost than the water tube boiler.
  • It has compact construction.
  • This boiler has a low risk of explosion.

Disadvantages of Fire Tube Boiler

  • It can’t produce high pressure.
  • It can’t generate a high rate of steam.
  • This type of boiler can generate pressure up to 20 bar, which is lower than a water-tube boiler.
  • It can’t use for high-pressure power plants.
  • The thermal efficiency of the fire tube boiler is up to 70% which is lower than the water tube boiler.
  • It can’t easily handle the load fluctuation.

Fire Tube Boiler Vs Water Tube Boiler

The main difference between the water tube boiler and fire tube boiler is given below:

Fire Tube Boiler  Water Tube Boiler
In the fire tube boiler, the water flows outside the fire tubes while hot gases move inside the fire tubes.In the water tube boiler, the flue gases flow outside the tubes while water flows inside the tubes.
This boiler has a high maintenance cost.This boiler has a low maintenance cost.
It can generate steam pressure up to 20 bar.It can generate pressure from 70 bar to 100 bar.
It is less efficient.It is more efficient.
This boiler is best for medium or low-pressure applications.This boiler is best for high-pressure applications.
A fire-tube boiler can’t produce pressure as high as a water tube boiler.A water tube boiler produces high pressure.
It has a low rate of steam generation.It has a high rate of steam generation.
This is an internally fired boiler. This is an externally fired boiler.
It has difficult construction.It has simple and easy construction.
This boiler needs a large diameter for the shell because the fire tubes are installed into the shell. This type of boiler needs a small diameter of the shell.
It uses for small and medium pressure applications such as marine, textile industries, and sugar mills.It uses for large steam pressure applications such as refining, paper, and pulp industries.
The cleaning and repairing of the fire tube boiler are very easy. The cleaning and repairing of the water tube boiler are very complicated. 
The fire-tube boilers are easy to operate.A skillful person is needed for the operation of the water tube boilers. 
It needs more space for installation.It needs less space for installation. 
There is a lower risk of explosion because it produces low pressure of steam.It has a high risk of burst because it produces high steam pressure.
These boilers have a high weight; they can’t shift easily from one place to another.They have low weight and can easily transport from one place to another.
The overall efficiency of the fire tube boiler is up to 75%.The overall efficiency of the water tube boiler is up to 90%.
The locomotive boiler and Lancashire boiler are examples of the fire tube boiler.  Stirling boiler, Lamont boiler, Benson boiler, Yarrow boiler, and simple vertical boiler are examples of water tube boiler.

Fire Tube Boiler Applications

  • The fire tube boilers are best for small-scale industries.
  • They are used in railways.
  • These types of boilers also use for marines and small hydroelectric power plants

FAQ Section 

What is meant by fire tube boiler?

A boiler in which the fire tubes submerge in the water and flue gases flow inside the fire tubes is called a fire tube boiler.

What is the example of the fire tube boiler?

The fire-tube boilers have the following examples:

  1. Lancashire Boiler
  2. Locomotive Boiler
  3. Cochran Boiler
  4. Cornish Boiler

What are fire tube boilers used for?

The fire-tube boilers are used for low pressure and low steam generation applications such as sugar mills, pulp and paper industries, chemical and small power plants.

Why is economizer used in boiler?

The main purpose of the economizer is to reduce fuel consumption according to the steam requirements.

It adds the heat transfer surface area inside the boiler and reduces the thermal stress.

Read More
  1. Different Types of Boilers
  2. Working of Lancashire Boiler
  3. Working of Lamont Boiler
  4. How to Perform Boiler Service

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